In many applications there is a need for controlled release of a substance to a medium. This need has in the past been addressed by encapsulating the substance in particles which release the substance over time. It has been a challenge to accurately control the rate of release of the substance to the medium. A further challenge is to introduce a delay period for release of the substance. Such a delay period may, for example, be desirable in cases where some time is required for the particles containing the substance to reach their desired destination in order to release the substance in the most effective location. Such a delay may also be desirable for the sequential delivery of multiple active substances each at different timepoints in the patient's treatment regime, or for cyclic delivery of multiple different hormones.
The present invention is designed to at least partially satisfy the above stated needs.